In most of nature there are usually multiply reasons why some behavior or action takes place.

Why do some eaqles make several nests? In other active territories only one nest is ever found. Obviously some make a new nest to replace one that has been destroyed by the weather. The nest used for several years very successfully, simply rotted out and fell, partially or wholly to the ground. In other cases the tree blew over. In many of the urban areas the availability of strong cedar, Sitka spruce or